package org.bouncycastle.pqc.crypto.mldsa;

import org.bouncycastle.util.Arrays;

class Ntt
{
    static final int[] nttZetas = {
        0, 25847, -2608894, -518909, 237124, -777960, -876248, 466468,
        1826347, 2353451, -359251, -2091905, 3119733, -2884855, 3111497, 2680103,
        2725464, 1024112, -1079900, 3585928, -549488, -1119584, 2619752, -2108549,
        -2118186, -3859737, -1399561, -3277672, 1757237, -19422, 4010497, 280005,
        2706023, 95776, 3077325, 3530437, -1661693, -3592148, -2537516, 3915439,
        -3861115, -3043716, 3574422, -2867647, 3539968, -300467, 2348700, -539299,
        -1699267, -1643818, 3505694, -3821735, 3507263, -2140649, -1600420, 3699596,
        811944, 531354, 954230, 3881043, 3900724, -2556880, 2071892, -2797779,
        -3930395, -1528703, -3677745, -3041255, -1452451, 3475950, 2176455, -1585221,
        -1257611, 1939314, -4083598, -1000202, -3190144, -3157330, -3632928, 126922,
        3412210, -983419, 2147896, 2715295, -2967645, -3693493, -411027, -2477047,
        -671102, -1228525, -22981, -1308169, -381987, 1349076, 1852771, -1430430,
        -3343383, 264944, 508951, 3097992, 44288, -1100098, 904516, 3958618,
        -3724342, -8578, 1653064, -3249728, 2389356, -210977, 759969, -1316856,
        189548, -3553272, 3159746, -1851402, -2409325, -177440, 1315589, 1341330,
        1285669, -1584928, -812732, -1439742, -3019102, -3881060, -3628969, 3839961,
        2091667, 3407706, 2316500, 3817976, -3342478, 2244091, -2446433, -3562462,
        266997, 2434439, -1235728, 3513181, -3520352, -3759364, -1197226, -3193378,
        900702, 1859098, 909542, 819034, 495491, -1613174, -43260, -522500,
        -655327, -3122442, 2031748, 3207046, -3556995, -525098, -768622, -3595838,
        342297, 286988, -2437823, 4108315, 3437287, -3342277, 1735879, 203044,
        2842341, 2691481, -2590150, 1265009, 4055324, 1247620, 2486353, 1595974,
        -3767016, 1250494, 2635921, -3548272, -2994039, 1869119, 1903435, -1050970,
        -1333058, 1237275, -3318210, -1430225, -451100, 1312455, 3306115, -1962642,
        -1279661, 1917081, -2546312, -1374803, 1500165, 777191, 2235880, 3406031,
        -542412, -2831860, -1671176, -1846953, -2584293, -3724270, 594136, -3776993,
        -2013608, 2432395, 2454455, -164721, 1957272, 3369112, 185531, -1207385,
        -3183426, 162844, 1616392, 3014001, 810149, 1652634, -3694233, -1799107,
        -3038916, 3523897, 3866901, 269760, 2213111, -975884, 1717735, 472078,
        -426683, 1723600, -1803090, 1910376, -1667432, -1104333, -260646, -3833893,
        -2939036, -2235985, -420899, -2286327, 183443, -976891, 1612842, -3545687,
        -554416, 3919660, -48306, -1362209, 3937738, 1400424, -846154, 1976782
    };

    static int[] ntt(int[] a)
    {
        int[] r = Arrays.copyOfRange(a, 0, a.length);

        int len, start, j, k;
        int zeta, t;

        k = 0;
        for (len = 128; len > 0; len >>>= 1)
        {
            for (start = 0; start < MLDSAEngine.DilithiumN; start = j + len)
            {
                zeta = nttZetas[++k];
                for (j = start; j < start + len; ++j)
                {
                    t = Reduce.montgomeryReduce(((long)zeta * (long)r[j + len]));
                    r[j + len] = r[j] - t;
                    r[j] = r[j] + t;
                }
            }
        }
        return r;
    }


    static int[] invNttToMont(int[] a)
    {
        int start, len, j, k;
        int t, zeta;
        final int f = 41978; // (mont^2)/256

        int[] out = Arrays.copyOfRange(a, 0, a.length);

        k = 256;
        for (len = 1; len < MLDSAEngine.DilithiumN; len <<= 1)
        {
            for (start = 0; start < MLDSAEngine.DilithiumN; start = j + len)
            {
                zeta = (-1) * nttZetas[--k];
                for (j = start; j < start + len; ++j)
                {
                    t = out[j];
                    out[j] = t + out[j + len];
                    out[j + len] = t - out[j + len];
                    out[j + len] = Reduce.montgomeryReduce((long)((long)zeta * (long)out[j + len]));
                }
            }
        }

        for (j = 0; j < MLDSAEngine.DilithiumN; ++j)
        {
            out[j] = Reduce.montgomeryReduce((long)((long)f * (long)out[j]));
        }
        return out;
    }
}

